Is there a gay brain? The neuroscience of homosexuality

Summary

This video by "This is your brain on science" explores the intriguing question of whether there's a distinctive "gay brain." The presentation delves into neurodevelopmental theories rather than evolutionary ones, focusing on brain development differences between heterosexuals and homosexuals. The video highlights various brain structures and functions associated with sexual behaviors and how these may vary by sexual orientation. It points to both prenatal hormonal influences and genetic components as potential factors influencing sexual orientation, offering a fun and engaging dive into the science behind the homosexual brain.

Highlights

• Explores the concept of a 'gay brain' and its complexities 🧐.
• Discusses how prenatal hormone exposure impacts sexual orientation 🎯.
• Highlights anatomical brain differences in areas like the hypothalamus and amygdala 🎢.
• Explains cognitive differences between sexual orientations, often mirroring gender differences 👀.
• Concludes that both genetics and prenatal development play roles in determining sexual orientation 🎨.

Key Takeaways

• The idea of a 'gay brain' is rooted in differences in brain structure and neural activity between sexual orientations 🧠.
• Hormones play a crucial role in brain development and can influence sexual orientation through prenatal experiences 🌈.
• Cognitive differences between sexual orientations mirror those between sexes, with gay men often showing traits similar to straight women and vice versa 🔄.
• Hypothalamic differences are key in understanding sexual arousal and behaviors, showing variance between gay and straight individuals 🚀.
• There is still much to uncover about how prenatal hormone influences and genetics uniquely shape sexual orientation in individuals 🧬.

Overview

Have you ever wondered if there's such a thing as a 'gay brain'? This fascinating dive into neuroscience tackles exactly that! Presenting theories beyond just evolutionary, this video focuses on neurodevelopmental aspects. From womb development to adult brain structures, the discussion fluidly connects hormones, genetics, and sexual orientation.

The presentation cleverly uses neuroscience to unveil how hormones might influence brain development, paving the way for a deeper understanding of sexual orientation. Particular brain regions like the hypothalamus and amygdala reveal stark differences between homosexual and heterosexual individuals, underlining the intricate web of our brain functions.

What's captivating is how sexual orientation shows cognitive parallels with the opposite gender, intriguing visual-spatial processing, and verbal fluency results. While unsurprisingly complex, these findings open the door to a tantalizing possibility: our brains might just reveal more about our sexual orientation than we ever imagined!

Is there a gay brain? The neuroscience of homosexuality Transcription

• 00:00 - 00:30 the vast majority of any population of people are heterosexual attracted to members of the opposite sex however some people homosexuals are attracted to members of the same sex estimates vary between anywhere around 1 to 6% of the general population depending on how and where you ask people now at this point in time it's it's well established that being gay is neither an act of choice nor something that you can successfully change in adulthood and so this leaves
• 00:30 - 01:00 us with a number of interesting questions like why are some people gay and some people not what is it about being a homosexual that leads them to have sexual orientations different from the rest of the general population well it's undeniable that behavior is critically linked to brain function and when it comes to sexual behavior this is no different the production of hormones the perception of Attractive people and the feeling of pleasure associated with sex these are all functions of the brain and so one interesting question that we can ask is
• 01:00 - 01:30 are there differences in brain structure or maybe in the patterns of neural activity between heterosexuals and homosexuals that can explain differences in sexual orientation or to put it much more simply is there a distinctly gay [Music] brain well the short answer is that yes there is but it's far more interesting
• 01:30 - 02:00 to cover exactly how and why so the first thing I'm going to do is cover theories about why people become homosexuals not evolutionary theories but neurodevelopmental ones and so that's going to involve a brief description of the brain development in the womb as well as sexual differentiation between males and female or male and female fetuses then I'm going to talk about what we know about the physical differences that exists in the brain of adult uh hetero and homosexuals specifically in brain brain regions important for sexual behavior
• 02:00 - 02:30 and attraction however um what you are attracted to is not the only thing that differs between homosexuals and heterosexuals um in the same way that men and women show differences in cognitive ability like verbal fluency mental rotation mathematics and abstract thought differences also exist between sexual orientations and so I'll talk a little bit about those and how those might might relate to differences in brain function in the end I'll attempt to bring it all together and form a kind of cohesive picture of the homosexual brain
• 02:30 - 03:00 so let's begin everybody starts out exactly the same as a little bundle of cells inside your mother's womb over the course of your time in the womb you will undergo several developmental changes that will take you from this little bundle of cells into a full-fledged baby and this developmental process is incredibly well documented for anybody who's interested in it sex differentiates uh from from around 6 to 12 weeks now it's widely
• 03:00 - 03:30 known that males have an XY chromosome and females have an XX chromosome and that these play a special role in determining biological sex one specific gene on the male Y is called the SR y or the sex determining region of Y and it starts the whole process off with a bang and it initiates testicle formation and without the sry Y well you get ovaries the presence of testosterone from the testes or the lack thereof with the ovaries results in a series of sex
• 03:30 - 04:00 specific characteristics in the developing brain the result of sexual differentiation creates a sex specific hormone environment in which the brain develops hormones like testosterone estrogen and progesterone act on the brain through receptors on brain cells and while the brain is beginning to grow in form the degree to which different hormones are present will influence how the brain grows and develops a brain with lots of testosterone surrounding it will grow differently than a brain with low testosterone surrounding it and this
• 04:00 - 04:30 is the basis for many sex differences in brain structures between men and women but where does homosexuality come to all of this well it is the separation in time between the development of physical sexual differences early on and neural sexual differences later on that leads to a sex-typical body male or female but not sex typical thoughts and behaviors you can develop into a perfectly typical physical male but if something happens to the developmental
• 04:30 - 05:00 process after this you may develop a male atypical brain now how might this happen well as of now no one knows exactly for sure and so there are many different theories early theories claimed that low testosterone in male fetuses caused homosexuality and high testosterone in female fetuses caused lesbianism there's plenty of evidence to show that this is in fact the case with women although not so much with men since high testosterone exposure in
• 05:00 - 05:30 utero can still produce homosexuality and so some people have suggested that it's not about how much testosterone um but about when testosterone effects happen over the course of pregnancy another commonly talked about effect is the birth order effect uh the more older brothers a person has the higher the likelihood of them turning out to be gay uh this only works with males however um and it's thought that it has to do with the mother producing antibodies against the male fetus and that these anti bodies alter the development of the male
• 05:30 - 06:00 brain a very strange but interesting idea some things that have been shown to increase the likelihood of having a gay child are things like diethyl still Bool an endocrine disrupting medication that has several uses like treating menopause however it was given to pregnant women thinking that it would reduce the risk of miscarriage it instead produced a number of adverse side effects in male sexual development to give you an idea as to the nature of dith still Bool it's used to chemically
• 06:00 - 06:30 castrate sex offenders taking thyroid hormone treatment while pregnant uh as well as some drugs like smoking cigarettes and amphetamine have been shown to increase homosexuality in children and of course stress has a large role in the hormone production and so there's a possibility that stressful events that occur to a pregnant mother at some critical point during her pregnancy could alter the organization of the baby's brain to lead to homosexuality the how and why of prenatal hormone influence on sexual
• 06:30 - 07:00 orientation is still incomplete and pretty complicated now I don't want you to think that the reason why people are gay is because you know their moms screwed up their pregnancy and homosexuality is simply a kind of brain impairment due to bad life decisions there's good evidence to indicate that homosexuality is at least in some part genetic and travels along distinct Family Lines complicating things even further so one way of conceiving of the cause of homosexuality is that there is
• 07:00 - 07:30 a genetic component that may predispose an individual to becoming homosexual that sets up their early development in such a way that only under some in utero circumstances like the ones we talked about uh that influence sex hormones will the developmental changes occur in the brain to result in a homosexual orientation and behaviors in adulthood now we can imagine two scenarios one in which a baby with for lack of a better term straight genes has something happened to them in utero and they turn out gay in adulthood and the second
• 07:30 - 08:00 scenario in which a baby with gay genes undergo a perfectly healthy development and so well turns out gay and it's because of all this that babies are thought to be born gay or straight although it's not quite as simple as that because you know babies don't just burst out of the womb fabulous right there's two important developmental periods in which sex hormones play well very important roles the first is during development in the womb like we just talked about and the second is of course puberty this is recognized as the
• 08:00 - 08:30 organizational activational effect of sex hormones in biology basically the first wave of hormones organizes the brain during development and once the baby is born hormones calm down for several years and then once puberty hits they Rise Again activating all of the relevant neural processes that were organized over a decade earlier uh this is why you might be in a sense born gay but you're not going to find out till much later so what exactly are the brain differences between homosexual and
• 08:30 - 09:00 heterosexuals well there are a number of differences between gay and straight brains in both men and women here's a list of some of the differences found so far over the next few minutes I'll go over each of these individually one of the first differences found in the brains of homosexuals is that of the anterior hypothalamus the hypothalamus is a very important brain structure as it links brain activity with hormone release
• 09:00 - 09:30 now of course hormones do a wide variety of things and so the hypothalamus does a wide variety of things as well ranging from Thermo regulation uh to thirst to sexual behavior the anterior portion is involved in the production of hormones related to sex attachment and sleep two parts in particular have been found to be different in male gay and straight brains the first is the Supra chiasmatic nucleus or scen because that's a bit of a mouthful and it's twice as large in homosexual men as
• 09:30 - 10:00 heterosexual men the other is the sexually dimorphic nucleus uh which is much smaller in homosexuals compared to heterosexual men because the hypothalamus plays an important role in sexual arousal and sexual behavior it's under understandable why there might be differences there now one major source of input to the hypothalamus is the amydala the amydala are a pair of almond shaped structures that are thought to code for emotional memories when you engage with an object
• 10:00 - 10:30 or an event and something happens that produces an emotional response like pleasure or pain or fear or anger the amydala will store memories of the emotional nature of the thing or the event being related to emotional memory they're also critical in the production of of emotional responses and the feeling of emotion two of them one on the left and one on the right and it has been shown that connectivity of the amigdala is different between men and women and heterosexuals and homosexuals ual homosexual men and heterosexual
• 10:30 - 11:00 women have more widespread Connections in their left amydala with homosexual women and heterosexual men having more widespread Connections in the right amydala the third difference occurs in the connection of the brain's two hemispheres the brain has two sides and those two sides are connected to each other through a series of fibers called commers one in particular is the anterior commer which connects the amydala as well as the temporal globes in homosexual men the anterior
• 11:00 - 11:30 commissure is much larger than in heterosexual men although this finding has been highly debated in the past interestingly many of the differences between orientations match the differences between the Sexes but in the opposite direction or simply put gay men tend to have brains like straight women and gay women brains like straight men at least in these specific brain areas now what exactly all of these differences mean uh and how they
• 11:30 - 12:00 contribute to differences in sexual orientation is somewhat unknown but it's likely that they have an effect on how the brain processes sexual information so now I'm going to talk about brain circuits that are dedicated to sexual behavior and how they are differently activated in heterosexuals and homosexuals in all people there is what we might call a sexual attraction circuit or maybe circuits would be a better way of putting it because there's a whole bunch of different things going
• 12:00 - 12:30 on and these are brain areas responsible for per receiving sexual images creating a sense of Attraction and arousal and then moving towards whatever we find attractive in a sexually appropriate way briefly there is a visual system involved in perceiving sexual images two areas in particular the extra striate body area that responds to images of bodies and the human form and is critical in identifying the human shape and the fusiform face area which does well
• 12:30 - 13:00 exactly the same thing but with regards to faces now there is a widely known but maybe not so widely understood Reward Center in the brain this focuses largely on the striatum and utilizes dopamine in response to food drugs pleasurable things and of course sexual partners many cortical areas are connected with the striatum that regulate these functions and then there is a motor planning system which plans out behaviors that you want to engage in of course when you see something sexual you
• 13:00 - 13:30 don't just sit there you know you want to have sex with it and so parts of the parietal cortex and premotor cortex do just that they plan out and coordinate movements together these three systems make up an extensive network of brain areas dedicated to sexual attraction among of course many other things research has shown that each of these three parts of this sexual system will become active when you see sexual images but specifically Ally when you see
• 13:30 - 14:00 images of the type that your preference would predict meaning that the opposite sex lights up the heterosexual brain in these areas and the same sex lights up homosexual brains in these areas one thing that has been done that highlights this even more which I think is quite interesting is that the sweat of males and females contain testosterone and estrogen like compounds that are thought to be human pheromonal signals pheromones are chemicals that animals send off of their bodies and the air that other animals of the same species
• 14:00 - 14:30 can detect when you smell these compounds certain areas of the hypothalamus become activated this happens when straight men smell female chemicals and straight women smell the male compounds the opposite is true of homosexuals in exactly the way that you would expect and predict gay men's hypothalamus becomes active in the presence of men's sweat and the men's pheromones and gay women with women's sweat and women's pheromones together all of this highlights the idea that much of the
• 14:30 - 15:00 attraction circuitry is the same uh in most people but that it's what activates it that is different and of course all this brain activity is closely related to hypothalamic function which as we mentioned earlier is structurally different between heterosexuals and homosexuals now anybody who's ever met gay people uh they know that there's many things that are different about them and it's not like it's just their attraction to the same sex and that's it um a lot of work has been done indicating that there are cognitive differences between sexual orientations
• 15:00 - 15:30 as well cognitive testing has shown us that there are differences between the Sexes but also differences between the orientations in the opposite direction here's a nice little chart I compiled of some of the main ones or the big ones that people know about men tend to be better than women at mental rotation and spatial perception uh but worse at verbal fluency the same is true when you compare hom seexual men to heterosexual
• 15:30 - 16:00 men and homosexual women to heterosexual women or in other words gay men perform like straight women and gay women perform like straight men some functional Imaging work has been done that may explain some of these differences in a study of resting state fmri it was shown that gay men had less activity in the supplementary motor area shown here this area is thought to be necessary for planning movements and so is critical in mental rotation tasks homosexual men also had less activity in
• 16:00 - 16:30 the left occipital gyrus and left middle temporal gyrus seen here compared to straight men an area thought to be critical in visual spatial processing and may contribute to the differences seen in spatial perception tasks and finally straight men have been shown to have more activity in their left brain than the right brain in the supramarginal gyrus an area important in verbal understanding one theory is that men have verbal function mostly on their left sides of their brain while women
• 16:30 - 17:00 have functioned more bilaterally or on both sides homosexual men have reduced activity in the left super marginal gyrus compared to straight men indicating that this might be the case and that their brains at least with verbal fluency perform more like straight women's than straight men's collectively all of the research that I've talked about so far points to the idea that disruption of normal gatal sex hormone function affects the organization of brain during development in utero and that this changes the
• 17:00 - 17:30 structure of the hypothalamus to be responsive to the same sex as opposed to the opposite sex the organization of other brain regions most notably cortical development will tend towards female typical organization and the sexual functions of the hypothalamus will be more female than male now at least in some brain regions it appears that homosexuals have brain structures and functions more like the heterosexual orientation of the opposite sex while still maintaining the physical bodies of their given body biological sex now
• 17:30 - 18:00 importantly all of the information that I've covered here is not mine I do not have the time or the money to run hundreds of experiments uh all that I've done today is uh show you the results of hard work from neuroscientists over the years this is simply my presentation so if you're interested in learning more then please check out the links and references that I've got in the low bar and as always thank you for watching and have a wonderful day